<%@ page contentType="image/jpeg"
         import="java.awt.*,
java.awt.image.*,java.util.*,javax.imageio.*"  pageEncoding="utf-8" %>
<%!
    public static String code="abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    Color getRandColor(int fc,int bc){//给定范围获得随机颜色
        Random random = new Random();
        if(fc>255) fc=255;
        if(bc>255) bc=255;
        int r=fc+random.nextInt(bc-fc);
        int g=fc+random.nextInt(bc-fc);
        int b=fc+random.nextInt(bc-fc);
        return new Color(r,g,b);
    }
%>
<%
    out.clear();//这句针对resin服务器，如果是tomacat可以不要这句
//设置页面不缓存
    response.setHeader("Pragma", "No-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expires", 0);
// 在内存中创建图象,设置图片的显示大小
    int width = 60, height = 20;
    BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
// 获取图形上下文
    Graphics g = image.getGraphics();
//生成随机类
    Random random = new Random();
// 设定背景色
    g.setColor(getRandColor(200, 250));
    g.fillRect(0, 0, width, height);
//设定字体
    g.setFont(new Font("Lnk Free", Font.PLAIN, 18));
//画边框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);
// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到

    for (int i = 0; i < 50; i++) {
        g.setColor(getRandColor(0, 255));
        int x = random.nextInt(width);
        int y = random.nextInt(height);
        int xl = random.nextInt(12);
        int yl = random.nextInt(12);
        g.drawLine(x, y, x + xl, y + yl);
    }
// 取随机产生的认证码(由数字和字母组长的)
    String sRand = "";
    for (int i = 0; i < 4; i++) {
        int rand = random.nextInt(62);
        sRand += String.valueOf(code.charAt(rand));
// 将认证码显示到图象中
        g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
        g.drawString(String.valueOf(code.charAt(rand)), 13 * i + 6, 16);
    }
// 将认证码存入SESSION
    session.setAttribute("rand", sRand);
// 图象生效
    g.dispose();
// 输出图象到页面
    ImageIO.write(image, "JPEG", response.getOutputStream());



%>